Chronology,Geochemistry And Rock Genesis Of Potassium-ultra-potassium Volcanic Rocks In The Temple Group Of The Middle Section Of Lhasa Block

The Qinghai-Tibet Plateau is the product of the continuous convergence of the Indian and Eurasian plates and is the natural Laboratory for the study of the global orogenic process.Chaz area is located in the hinterland of the Qinghai-Tibet Plateau,located in the southern foothills of Gangdise Shan,located in Rikaze Angren County Chaz Township,Amu Xiong Township Territory is distributed a large number of potassium-ultra-potassium magmatic rocks.This paper mainly takes Chaz Township and surrounding areas as the main research work area,selects the potassium-super-potassium rock in the study area as the research object,carries on the chronology,the Petrology and the main trace rare earth Element Research analysis,discusses the potassium-potash rock Genesis and the regional tectonic evolution characteristic in the Chaz Township area,It provides a new scientific basis for the study of the evolution process formed by the Qinghai-Tibet Plateau.The chronological study of potassium-Chaz rocks in the region shows that the age range of basal volcanic rocks is concentrated among 9.46-12.92Ma,and the formation of the Times is Miocene.According to the previous research data,it is generally believed that 40Ma³0Ma is the peak of magmatic action,and its diagenesis time is later than the peak of magmatic action,which belongs to the product of post-collision magma in Qinghai-Tibet plateau.The Chaz volcanic rocks in the middle of the region are mainly coarse-sided andesite and black mica,the content of SiO₂ is 51.63%-63.52%,alkali-rich,the content of total alkali?Na₂O+K₂O?is 8.22%-9.67%,K₂O content is 5.93%-7.19%,and the rock has the characteristics of obvious alkali-rich and high potassium.The content of K₂O/Na₂O 2.58%-2.93%,belongs to the super-potassium rock series.The abundance of rare earth elements is between 536.86x10-6-854.52x10-6,which reflects the degree of gravity of rare earth fractionation?LA/YB?n ratio between 36.89-41.63,indicating that the weight of rare earth elements fractionation is obvious.The right-leaning distribution type with obvious light rare earth enrichment.The?Eu value is 0.55-0.66 and has a slight negative europium anomaly,which indicates that there has been no significant effect of oblique feldspar separation and crystallization during magmatic evolution.After testing,it was found that it has the characteristics of rich and large ionic hydrophilic elements Rb,Th,Ba,U,K,at the same time has a loss of high field strength elements Nb,Ta,Ti.With the consistent distribution type of trace elements,the total abundance of radioactive thermal elements and large ionic pro-stone elements is high,which constitutes a score curve with a significant tilt to the right.The negative anomaly elements are Sr,P,which shows that there may be crystallization differentiation of pyrite,apatite and other minerals in the process of magmatic evolution.Based on the Rock series,chronology characteristics and geochemical characteristics of volcanic rocks in the Chaz region,it is pointed out that a series of Miocene volcanic rocks appear in the area,the material source area may be:The Indian mainland and Eurasia collide,so that the area of the continental crust thickening,the formation of Shangen,while the lithosphere is also thickened.At the same time,crustal matter enters the lithosphere mantle by ancient subduction and undergoes long-term evolution and becomes the rich mantle of shell source material.Subsequently,under the influence of North-south extrusion and east-west tensile tensor,the bottom of the plateau lithosphere occurred,resulting in the soft flow coil material upwelling,and eventually triggered the formation of potassium-ultra-potassium magma action.